Sensor system for a vacuum deposition apparatus

ABSTRACT

Apparatus for accurately determining, continuously, the coating thickness deposited on an article during a vapor deposition process. The apparatus utilizes a unique pickup plate and straingauged cantilever beam positioned within the vacuum chamber to continuously record the coating thickness deposited on the article.

0 United States Patent 1111 3,570,449

[72] Inventors Sol S. Blecherman [56] References Cited UNITED STATES PATENTS Mitchell J. Bala, Hazardville; Robert B. s 4 660 2 1952 B f 117 107 l Lougee,Windsor' Johannes Grafwallner aricrot l X South Glastonbu Conn 2,746,420 5/1956 Ste1gerwa1d 118/49X [21] A l No 806 951 3,086,889 4/1963 Strong ll8/49X [22] f 13 1969 3,329,601 7/1967 M666 118/49.sx [45] Patented 1611971 3,347,701 10/1967 Yamagishiet a1. 118/49.1X [73] Assignee United Aircraft Corporation gnzlcker etlal 118, 49X East Hartford Comb v ccary eta 164/250X 3,453,984 7/1969 Gerek 118/8- FOREIGN PATENTS I 1,051,402 12/1966 Great Britain l18/49.5 s41 SENSOR SYSTEM FOR A VACUUM DEPOSITION APPARATUS Attorney-James A. Kane 10 Claims, 1 Drawing Fig. [52] I US. Cl .Q. 118/9, ABSTRACT: Apparatus for accurately determining, continu- 1l8/49.5, 164/49 ously, the coating thickness deposited on an article during a [51] Int.Cl C23e 13/08 vapor deposition process. The apparatus utilizes a unique [50] Field of Search l18/l,6, 7, pickup plate and strain-gauged cantilever beam positioned 8, 9; 1 17/(COntro1 Digest), 106- 107.2 Dated); 164/49; 33/(lnquired); 73/(Inquired) within the vacuum chamber to continuously record the coating thickness deposited on the article.

Patented March 16, 1971 3,570,449"

SENSOR SYSTEM FOR A VACUUM DEPOSITION APPARATUS BACKGROUND OF THE INVENTION The present invention relates to metal-coating process and more particularly to vacuum deposition of a coating on a substrate.

The coating of substrates by evaporation of the coating alloy of two or more components or constituents requires that an equilibrium be maintained between the solid ingot and molten pool and the vapors which leave the pool. If this equilibrium is maintained, coatings of constant and reproducible chemistry will be produced, and the ability to deposit a coating of uniform thickness on a substrate will be achieved. One method for achieving thickness control on substrates of vapor deposited coatings is by an in-process collection weighing of evaporated materials in close proximity to the substrate. Monitoring crystal resonance changes is anothertechnique used in the prior art, particularly in thin film vacuum deposition processes. This technique, however, cannot be used effectively for thick coatings, i.e., coatings. greater than 0.001 inch, and since thick vacuum-coating systems are relatively unknown, the problem of controlling the coating thickness which is deposited on a substrate and which is relatively thick has been an essentially unexplored area in the prior art.

SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a sensor system or sensor means that permits the highly accurate determination of weight accumulated or material deposited on a substrate continuously in a vacuum deposition production system, whether the coating is relatively thin or relatively thick One feature which permits this highly accurate determination of weight accumulated or deposited on a substrate, and hence control of the thickness of vapor deposited on the substrate, is the use of a suspension system and unique pickup plate or collection surface which insures lateral and vertical plane stability whileexperiencing force changes due to changes in vapor flow intensity. Another feature of the present invention is the utilization of a strain-gauged cantilever beam to provide maximum weight pickup without compromising accuracy. Additionally, the geometry of the cantilevered beam is that of a twisted beam'which thereby improves the rigidity characteristics of the suspension system. Another feature is the use of a coolant scheme around the cantilever beam to minimize the temperature variation effects inherent in strain gauge sensor applications. Finally the sensor system of the present invention utilizes a signal output system which presents a continuous display of the coating thickness deposited on the substrate during the vapor deposition process.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a vertical section view, diagrammatic, through a crucible and associated mechanism incorporating the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The arrangement is shown is an apparatus for the coating of articles by a metallic alloy in which the alloy is vaporized by use of an electron beam. Referring to the FIG., vacuum chamber 6 is shown as including an outlet or evacuation port S, port 8 being connected to a conventional vacuum pump,

herein not shown. As illustrated in the-drawing, the vaporizing alloy or source material is in the form of an ingot 10 extending upwardly into a water-cooled bottom-feed crucible 12. As the ingot It] is consumed, it is fed upwardly by a variable speed motor M driving, for example, through a reduction gear mechanism 16 to a pair of ingot feed rollers 18. The end of the ingot within the crucible is melted and vaporized by an electron beam 20 from a filament 22 forming part of an electron gun 24. The beam is focused directly on the end of ingot l0 and melts the surface of the ingot and vaporizes it into a moving cloud of vapor material.

Above the crucible in a position for deposition of vapor thereon is a substrate or article 30, shown as a turbine vane, and held in position on a support device 32, preferably equipped with a clamp 34 for releasable attachment of the article.

While it is obvious that the amount of coating thickness deposited on any substrate may be determined by the simple expedient of weighing before and after exposure to the vapor cloud, it is extremely desirable to be able to continuously monitor and hence determine the weight accumulation on the substrate. To this end, pickup plate 40 is positioned in the proximity of the substrate to be coated; therefore, the material to be deposited on the substrate will also be deposited on the pickup plate 40. The shape and configuration of the pickup plate are of extreme significance in that the pickup plate must be stable against the unsteady state momentum changes experienced during coating. Pickup plate 40 is substantially a dome-shaped member, and includes a collection surface 42 which faces ingot 10 that is substantially parabolic in shape. As a result of this parabolic shape, the vapors of the moving vapor cloud impinge on all surfaces thereof, and therefore, the resultant forces are directed toward the pickup plates axis of symmetry thereby providing lateral and horizontal stability.

Since the pickup plate is a simple shape, it's surface area is easily computed and the increase in weight of the plate for each established increment in coating thickness collecting on the plate is also easily determined. Accordingly, if the pickup plate has a surface-area, for example, of 4 square inches, it is easy to compute the weight of each .001 inch of coating deposited thereon during .the coating of the complex-shaped turbine vane. Thus with the pickup plate 40 the weight-sensing means, hereinafter described in detail is readily calibrated to indicate directly the thickness of the coating as it is being deposited on the substrate as well as on the pickup plate without the problem of computing the surface area of the specific part being coated.

Pickup plate 40 comprises a portion of the overall sensor system or means 38, which means permit the continuous determination of the amount of material, by weight, which is deposited on substrate or article 30. Sensor means 38 also includes a support or suspension means for pickup plate 40. Suspension means 44 as illustrated supports pickup plate 40 through cable 46, cable 46 extending to pickup plate 40 from beam 48, which is herein illustrated as having strain gauge 49 therein, the beam supporting pickup plate 40 from its relatively free or unsupported end. 7

Beam 48 is of a unique structure in that it is supported from beam holder 50 in cantilevered fashion, More specifically, the end remote from beam holder support means 51, that is, the end from which the pickup plate is supported is free to move in a vertical plane as material is deposited on pickup plate 40. The added material causes beam 4% to deflect or bend, this deflection causing the strain gauge signal of beam 48 to vary. This change or variance of the strain gauge signal is transmitted to a readout means 52, such as an X-Y plot on a strip chart recorder and the curve or plot is determinative of the amount of material deposited on the substrate.

Strain-gauged beam 4% is of a twisted beam construction, this construction being clearly illustrated in the drawing. As illustrated, the end of beam 48 supported at beam holder support means 511 faces outwardly with respect to ingot 10 while the end distal therefrom faces inwardly with respect to ingot 10. This type of beam construction improves the rigidity of the sensor system and is an aide to the stability characteristics of pickup plate 430.

Finally, to minimize any temperature effects on the sensor means, the cantilevered beam $8 is substantially isolated from the vacuum chambers hostile temperature environment by a liquid-cooled shroud and thermal shielding. As shown in the drawing, beam holder 50 includes thermal shield 56 and liquid inlet means 60 and liquid outlet means 58, these structural members serving to maintain the beam holder and beam at a substantially stable and controlled temperature.

We claim:

1. in a vapor deposition apparatus for use in coating articles:

a vacuum chamber in which an article may be positioned;

a source of coating material positioned within the chamber;

means for hearing the source material and creating a moving cloud of vapor above the source material;

means for supporting an article to be coated within the cloud area, and

sensor means including a pickup plate to be coated during coating of the article, said plate being adjacent to said article support means and also within the cloud area and connected by suspension means for continuously determining the amount by weight of material deposited on the article, the weight deposited on the sensor means being determinative of the coating thickness deposited on the article.

2. A vapor deposition apparatus as in claim 1 wherein; the pickup plate is substantially a dome-shaped member, and the vapor collection surface is substantially parabolic in shape.

3. In a vapor deposition apparatus for use in coating articles:

a vacuum chamber in which an article may be positioned;

a source of coating material positioned within the chamber;

means for heating the source material and creating a moving cloud of vapor above the source material;

sensor means including a pickup plate positioned in proximity to the article to be coated, a cantilever beam supporting said pickup plate and incorporating a strain gauge for sensing the weight of the pickup plate, the addition of any vapor deposited on the pickup plate varying the output signal of the strain gauge and the sensor means including means for continuously recording the signal from the strain gauge.

4. A vapor deposition apparatus as in claim 3 wherein;

one end of the strain-gauged cantilever beam is supported by a liquid-cooled beam holder.

5. A vapor deposition apparatus as in claim 4 wherein;

the strain-gauged cantilever beam is of a twisted beam construction, the end distal from the end supported in the beam holder being oppositely faced to the supported end with respect to the vapor source.

6. A coating apparatus for applying a metallic alloy to a substrate comprising:

a chamber in which the substrate may be mounted;

means for evacuating the chamber;

means for feeding a bar of alloy into a crucible mounted within the chamber;

a constant energy electron beam means for vaporizing the alloy in the crucible, the electron beam means thereby creating a moving vapor cloud between the crucible and the substrate, an alloy coating thereby being deposited on the substrate;

supporting means for positioning the substrate within the vapor cloud area, and

sensor means including a collecting plate located within the vapor cloud area and connected by suspension means for continuously determining the amount by weight of alloy material deposited on the substrate, the weight deposited on the sensor means being determinative of the coating thickness deposited on the substrate.

7. A vapor deposition apparatus as in claim 6 wherein;

the pickup plate is substantially a dome-shaped member, and the vapor collection surface is substantially parabolic in shape.

8. A coating apparatus for applying a metallic alloy to a substrate comprising:

a chamber in which the substrate may be mounted;

means for evacuating the chamber;

means for feeding a bar of alloy into a crucible mounted within the chamber; a constant energy electron beam means for vaporizing the alloy in the crucible, the electron beam means creating a moving vapor cloud between the crucible and the substrate for depositing an alloy coating on the substrate;

supporting means for positioning the substrate within the vapor cloud area, and

sensor means including a pickup plate positioned in proximity to the substrate to be coated and suspension means for the pickup plate for continually determining the amount of material deposited on the plate, said suspension means including a cantilever beam incorporating a strain gauge the addition of any vapor deposit on the pickup plate varying the output signal of the strain gauge and the sensor means including means for continuously recording the signal from the gauge.

9. A vapor deposition apparatus as in claim 8 wherein;

one end of the strain gauged cantilever beam is supported by a liquid-cooled beam holder.

10. A vapor deposition apparatus as in claim 8 wherein;

the strain-gauged cantilever beam is of a twisted beam construction, the end distal from the end supported in the beam holder being oppositely faced to the supported end with respect to the vapor source. 

1. In a vapor deposition apparatus for use in coating articles: a vacuum chamber in which an article may be positioned; a source of coating material positioned within the chamber; means for hearing the source material and creating a moving cloud of vapor above the source material; means for supporting an article to be coated within the cloud area, and sensor means including a pickup plate to be coated during coating of the article, said plate being adjacent to said article support means and also within the cloud area and connected by suspension means for continuously determining the amount by weight of material deposited on the article, the weight deposited on the sensor means being determinative of the coating thickness deposited on the article.
 2. A vapor deposition apparatus as in claim 1 wherein; the pickup plate is substantially a dome-shaped member, and the vapor collection surface is substantially parabolic in shape.
 3. In a vapor deposition apparatus for use in coating articles: a vacuum chamber in which an article may be positioned; a source of coating material positioned within the chamber; means for heating the source material and creating a moving cloud of vapor above the source material; sensor means including a pickup plate positioned in proximity to the article to be coated, a cantilever beam supporting said pickup plate and incorporating a strain gauge for sensing the weight of the pickup plate, the addition of any vapor deposited on the pickup plate varying the output signal of the strain gauge and the sensor means including means for continuously recording the signal from the strain gauge.
 4. A vapor deposition apparatus as in claim 3 wherein; one end of the strain-gauged cantilever beam is supported by a liquid-cooled beam holder.
 5. A vapor deposition apparatus as in claim 4 wherein; the strain-gauged cantilever beam is of a twisted beam construction, the end distal from the end supported in the beam holder being oppositely faced to the supported end with respect to the vapor source.
 6. A coating apparatus for applying a metallic alloy to a substrate comprising: a chamber in which the substrate may be mounted; means for evacuating the chamber; means for feeding a bar of alloy into a crucible mounted within the chamber; a constant energy electron beam means for vaporizing the alloy in the crucible, the electron beam means thereby creating a moving vapor cloud between the crucible and the substrate, an alloy coating thereby being deposited on the substrate; supporting means for positioning the substrate within the vapor cloud area, and sensor means including a collecting plate located within the vapor cloud area and connected by suspension means for continuously determining the amount by weight of alloy material deposited on the substrate, the weight deposited on the sensor means being determinative of the coating thickness deposited on the substrate.
 7. A vapor deposition apparatus as in claim 6 wherein; the pickup plate is substantially a dome-shaped member, and the vapor collection surface is substantially parabolic in shape.
 8. A coating apparatus for applying a metallic alloy to a substrate comprising: a chamber in which the substrate may be mounted; means for evacuating the chamber; means for feeding a bar of alloy into a crucible mounted within the chamber; a constant energy electron beam means for vaporizing the alloy in the crucible, the electron beam means creating a moving vapor cloud between the crucible and the substrate for depositing an alloy coating on the substrate; supporting means for positioning the substrate within the vapor cloud area, and sensor means including a pickup plate positioned in proximity to the substrate to be coated and suspension means for the pickup plate for continually determining the amount of material deposited on the plate, said suspension means including a cantilever beam incorporating a strain gauge the addition of any vapor deposit on the pickup plate varying the output signal of the strain gauge and the sensor means including means for continuously recording the signal from the gauge.
 9. A vapor deposition apparatus as in claim 8 wherein; one end of the strain gauged cantilever beam is supported by a liquid-cooled beam holder.
 10. A vapor deposition apparatus as in claim 8 wherein; the strain-gauged cantilever beam is of a twisted beam construction, the end distal from the end supported in the beam holder being oppositely faced to the supported end with respect to the vapor source. 